The Protective Effect Of Lycium Barbarum Polysaccharide Combined With Exercise On Liver Mitochondrial Function In Nonalcoholic Fatty Liver Rats

Objective Nonalcoholic fatty liver disease(NAFLD)has became the major chronic liver disease in the world,and its pathogenesis is closely related to mitochondrial oxidative stress and dysfunction.Studies have shown that Lycium barbarum polysaccharides(LBP)and moderate exercise can reduce oxidative stress and regulate lipid metabolism.This study will explore the protective effects of LBP combined with aerobic exercise on liver mitochondria in NAFLD rats from two aspects: mitochondrial oxidative stress and mitochondrial function.Methods 54 male SD rats were randomly divided into control group(n=12)and high-fat diet group(HFD)(n=42)according to their body weight,then fed with normal diet and HFD,respectively.After feeding the rats for 10 weeks,the average body weight was 20%higher than that of the control group and hepatocyte steatosis accounted for more than 1/3 of hepatic lobule were defined as a successful NAFLD model.Then the HFD group was randomly divided into 4 groups: HFD group,HFD+LBP group,HFD+Exercise(HFD+E)and HFD+LBP+E group.HFD+E and HFD+LBP+E group exercised on treadmill(20m/min,0°,60 min/d,5 d/w)for 8w.HFD+LBP and HFD+LBP+E groups were given LBP at a dose of 50mg/kg body weight per day,while group control,HFD and HFD+E were given the same volume of normal saline.Glucose tolerance test was performed at the end of the 7th week.After 8 weeks of intervention,serum were taken to determine total cholesterol(TC),triglyceride(TG),alanine aminotransferase(ALT),aspartate aminotransferase(AST),insulin level and insulin resistance index(HOMA-IR),and single cell suspension was made to detect the content of mitochondrial ROS.Liver mitochondria were extracted to detect malondialdehyde(MDA),8-hydroxy-2 deoxyguanosine(8-OHd G),glutathionease(GSH)and glutathione peroxidase(GSH-Px).Liver TG,TC,superoxide dismutase(SOD)activity and adenosine triphosphate(ATP)content were also detected.The ultrastructure and histopathological changes of liver were observed,and the relative expression levels of uncoupling protein-2(UCP2)and silencing information regulator 3(SIRT3)in liver tissue were detected by Western blot.Finally,the test results were sorted out and statistically analyzed.Results After 10 weeks of HFD feeding,the model of NAFLD rats was established successfully.Long-term HFD resulted in insulin resistance(IR),obesity,dyslipidemia,mitochondrial oxidative damage and dysfunction in NAFLD rats,liver mitochondrial protein UCP2 expression increased significantly,SIRT3 protein expression decreased.Compared with HFD group,a significant decrease was observed in the body weight,obesity index and visceral index of group HFD+E and HFD+LBP+E(P<0.05),while there was no significant difference of body weight and obesity index in group HFD+LBP.Moreover,the average levels of liver tissue TG,TC and serum TG,TC,ALT/AST ratio as well as HOMA-IR of 3intervention groups,except for serum TG and TC in HFD+LBP group,the others were significantly lower than group HFD(P<0.05).Compared with HFD group,the contents of ROS and MDA in mitochondria were significantly decreased(P<0.05 or P<0.01),while GSH,GSH-Px activity,SOD activity and ATP were increased in 3 experimental groups,except for SOD activity in group HFD+LBP.Compared with HFD group,the relative protein expression of UCP2 was decreased in group HFD+LBP and HFD+E,and it was significantly decreased in group HFD+LBP+E.The level of SIRT3 protein in 3 intervention groups were significantly higher than HFD group,and the level of SIRT3 protein in HFD+LBP+E group was significantly higher than group HFD+LBP.The microscopic structure showed that in group HFD,the hepatic cord was disordered,the hepatic sinusoid narrowed,and there were a large number of lipid droplet vacuoles appeared in hepatocytes,while the lipid droplet vacuoles were decreased and the hepatic cord was clear in HFD+LBP group.The microscopic structure of group HFD+E and HFD+LBP+E were closed to the normal structure.The ultrastructure showed that in HFD group,the number of mitochondria decreased,the morphology and structure were abnormal,mitochondrial cristae were broken and dissolved,and the mitochondrial membrane could not be identified.However,the structure of mitochondria was improved in all intervention groups,the number of mitochondria increased and the structure was normal in HFD+E group and HFD+LBP+E group.Conclusion A long-term HFD can lead to obesity,IR,oxidative damage of mitochondria,cause structural and functional abnormalities of mitochondria,and hepatic steatosis.LBP and aerobic exercise have synergistic effect,and their combined intervention can significantly improve ameliorate the lipid metabolism disorder and IR in NAFLD rats,reduce oxidative damage,protect the function of mitochondria and increase the number of mitochondria,and reduce the degree of hepatic steatosis.These changes may be mediated by down-regulate the expression of UCP2 and up-regulate the SIRT3 expression.